International Shipbuilding Progress - Volume 18, issue 205

Authors: van Oossanen, P.

Article Type: Research Article

Abstract: In this paper some indications are given as to how current propeller design practices may be modified to obtain improved cavitation properties for the moderately loaded screw propeller operating in a wake. Some general rules concerning the choice of propeller diameter, rotative speed, direction of rotation, blade area ratio, radial load distribution, etc. are discussed. The largest part of the paper, however, deals with a method to determine propeller pitch, blade thickness and camber in accordance with obtaining maximum latitude to variations in the angle of attack. It is postulated that for minimizing cavitation occurrence it is ineffective to determine …pitch, thickness and camber solely by means of providing for the required strength, the required lift and a non-cavitating condition at shock free entry of the flow. The variation in the angle of attack, an inherent property of the non-uniform velocity field in which the screw propeller works, must also be accounted for. By incorporating the outlined quasi-stationary blade section shaping method in modern propeller design, the proper compromise between the conflicting characters of thick sections (with large possible cavitation-free angle of attack variations) and thin sections (free of cavitation at low cavitation numbers at shock-free entry of the flow) is made. This paper is a further development and another result of continuous and persistant research carried out at the Netherlands Ship Model Basin into the adaptation of the propeller to the wake to obtain optimum results. Show more

DOI: 10.3233/ISP-1971-1820501

Citation: International Shipbuilding Progress, vol. 18, no. 205, pp. 321-333, 1971

Authors: de Wit, C.

Article Type: Research Article

Abstract: The author of this report was assigned to investigate the mathematical aspects of meteorological ship routeing by Prof. Dr. R. Timman of the Delft University of Technology. The assignment was accomplished in 1968, resulting in a doctor’s thesis, entitled “Mathematical Treatment of Optimal Ocean Ship Routeing” [1]. This report describes the outlines of this dissertation. The first section contains the problem statement as well as some notational conventions. In order to avoid metric difficulties, the navigated region G is to be mapped conformally onto a plane, keeping the scale alteration as small as possible. Section 2 gives a …curse treatment of the most important mappings that fit this purpose. In the 3rd section the minimal time problem is discussed as an application of Pontryagin’s optimal control theory. The concept of a timefront is introduced and some attention is given to possible structure complications of these fronts. Also modifications of the general theory, in the event that part of a trajectory should coincide with the boundary of the region G, are briefly mentioned. Section 4 cursely treats wave prediction methods and the determination of a ship’s behaviour in sea waves. In the 5th section the computer program to evaluate the least time track is described and the results of a practical application are exhibited. The consequences of data incertainties and the practical use of the treated method are briefly discussed. The two appendices contain mathematical treatments of the general minimal time problem and of the minimal time problem with co-ordinate restrictions. Show more

DOI: 10.3233/ISP-1971-1820502

Citation: International Shipbuilding Progress, vol. 18, no. 205, pp. 334-356, 1971